The present invention relates to an output amplifier, and more particularly to an output amplifier employed for an SEPP (Single Ended Push-Pull) power amplifier.
When a conventional output amplifying circuit is employed for an SEPP power amplifier which is arranged to perform a B or AB class operation, prestage circuits of output transistors of the output amplifying circuit are not immediately cut off even after the output transistors are cut off. This causes an operation lag between the operating condition of the output transistors and the operating condition of the prestage circuits, resulting in output waveform distortions.
In any arrangement of the conventional SEPP power amplifier of A, B or AB class, when no signals are generated (at idling), the idling current of the output transistors changes greatly when the bias current for the output transistors changes. Thus, setting and control of the idling current has been difficult.
The distortion problem mentioned above may be mainly encountered in semi-complementary SEPP power amplifiers when the circuits are formed by integrated circuits.